The present invention concerns an arrangement with a plurality of plug points and a plurality of plug-in functional units.
In stored-program controls, generally one or more central subassemblies and a plurality of functional subassemblies, for example subassemblies for digital or analog input and output of signals, are interconnected via a system bus having address, data, and control lines. The subassemblies are fitted into plug points of a central or expansion unit, and means for address coding and decoding are provided in order for the functional subassemblies to be addressed by the central subassemblies during read or write functions.
To allow address coding to be dispensed with, it is proposed in European Patent Application 0 486 818 to provide one line each between a control unit and individual modules of a control system. The control unit addresses the modules by transmitting different data words over these lines. An addressing system of this kind, in an arrangement with plug-in functional units, means that a special plug-in position which executes read and write accesses to other functional units must be provided for the functional unit.